The present invention relates to the field of packaging for respiring or biochemically active agricultural products and commodities such as fresh fruits, fresh vegetables, fresh herbs, and flowers (herein referred to collectively as produce or fresh produce) and more particularly to registered microperforations in packaging materials for use in modifying or controlling the flow of oxygen and carbon dioxide into and/out of a fresh produce container.
The quality and shelf life of many food products is enhanced by enclosing them in packaging that modifies or controls the atmosphere surrounding the product. Increased quality and longer shelf life result in fresher products for the consumer, less waste from spoiled produce, better inventory control, and appreciable overall savings for the food industry at both the retail and wholesale levels.
Modified atmosphere packaging (MAP) and controlled atmosphere packaging (CAP) are often used interchangeably in the industry, and much confusion exists on their exact meanings. Both refer to methods to control the atmosphere in the package. In the processed foods area, MAP is considered a static method for controlling the atmosphere whereby an initial charge of a specific gas composition, e.g. 30% CO2 and 70% N2, is introduced into a barrier container before sealing.
The oxygen transmission rate (OTR) of a film is expressed as cc O2/m2-day-atmosphere, where one atmosphere is 101325 kg/ms2. Generally, a barrier container is one that has an OTR of  less than 70 cc/m2-day-atm. The units describing the flow of a particular gas through a film are xe2x80x9cfluxxe2x80x9d, expressed as cc/day-atm.
For fresh produce, the primary means to extend quality and shelf life is temperature control. However, more than 50 years of evidence from industry practices on bulk storage of fresh fruits and vegetables in refrigerated controlled atmosphere storage rooms has shown that atmosphere control can contribute greatly to quality retention and shelf life. The use of MAP/CAP for fresh produce was a natural progression once packaging technology had advanced to include the production of non-barrier (often referred to in the industry as xe2x80x9cbreathablexe2x80x9d) materials.
The goal in fresh fruit and vegetable packaging is to use MAP/CAP to preserve produce quality by reducing the aerobic respiration rate but avoiding anaerobic processes that lead to adverse changes in texture, flavor, and aroma, as well as an increased public health concern. Aerobic respiration can be defined by the following equation:
(CH2O)n+nO2xe2x86x92nCO2+nH2O+heat
where O2 from the air is used to metabolize carbohydrate ((CH2O)n) reserves and in the process, CO2, and H2O are produced and heat is generated. For each respiring item, there is an optimum O2 and CO2 level that will reduce its respiration rate and thereby, slow aging and degradative processes. Different fresh produce items have different respiration rates and different optimum atmospheres for extending quality and shelf life.
The concept of passive MAP became common with the development of packaging materials with OTRs of 1085 to 7000 cc/m2-day-atm for fresh-cut salads. In passive MAP, the produce is sealed in packages made from these low barrier materials and allowed to establish its own atmosphere over time through produce respiration processes. Sometimes the package is gas-flushed with N2 or a combination of CO2 and N2, or O2, CO2, and N2 before sealing to rapidly establish the desired gas composition inside the package. Alternately, a portion of the air may be removed from the pack, either by deflation or evacuation, before the package is sealed, to facilitate rapid establishment of the desired gas content.
In CAP, the atmosphere in the package is controlled at well-defined levels throughout storage. CAP can take many forms, and may even involve enclosing gas absorber packets inside processed food barrier packages. For example, CO2 absorber sachets may be sealed inside coffee containers to absorb and control the level of CO2 that continues to be generated by the ground coffee. Sachets containing iron oxides are enclosed in barrier packages of fresh refrigerated pasta to absorb low levels of O2 entering the package through the plastic material.
CAP of fresh produce is just a more controlled version of MAP. It involves a precise matching of packaging material gas transmission rates with the respiration rates of the produce. For example, many fresh-cut salad packages use passive MAP as described herein. If the packages are temperature-abused (stored at 6-10xc2x0 C. or higher), O2 levels diminish to less than 1%, and CO2 levels can exceed 20%. If these temperature-abused packages are then placed back into recommended 3-4xc2x0 C. storage, the packaging material gas transmission rates may not be high enough to establish an aerobic atmosphere ( less than 20% CO2,  greater than 1-2% O2) so fermentation reactions cause off-odors, off-flavors, and slimy product. If the salad was in a CAP package, the O2 levels would decrease and CO2 levels increase with temperature abuse, but would be re-established to desired levels within a short time after the product is returned to 4xc2x0 C. storage temperatures.
Today, films made from polymer blends, coextrusions, and laminate materials with OTRs of 1085 to 14,000 cc/100 m2-day-atm are being used for packaging various weights of low respiring produce items like lettuce and cabbage. These OTRs, however, are much too low to preserve the fresh quality of high respiring produce like broccoli, mushrooms, and asparagus. In addition, existing packaging material OTRs for bulk quantities ( greater than 1 kg) of some low respiring produce are not high enough to prevent sensory quality changes during storage. Therefore, several approaches have been patented describing methods to produce packaging materials to accommodate the higher respiration rate requirements and higher weights of a wide variety of fresh produce items.
U.S. Pat. Nos. 4,842,875, 4,923,703, 4,910,032, 4,879,078, and 4,923,650 describe the use of a breathable microporous patch placed over an opening in an essentially impermeable fresh produce container to control the flow of oxygen and carbon dioxide into and out of the container during storage. Although this method works effectively, the breathable patch must be produced by normal plastic extrusion and orientation processes, whereby, a highly filled, molten plastic is extruded onto a chill roll and oriented in the machine direction using a series of rolls that decrease the thickness of the web. During orientation, micropores are created in the film at the site of the filler particles. Next, the microporous film must be converted into pressure sensitive adhesive patches or heat-seal coated patches using narrow web printing presses that apply a pattern of adhesive over the microporous web and die-cut the film into individual patches on a roll. These processes make the cost of each patch too expensive for the wide spread use of this technology in the marketplace. In addition, the food packer has to apply the adhesive-coated breathable patch over a hole made in the primary packaging material (bag or lidding film) during the food packaging operation. To do this, the packer must purchase hole-punching and label application equipment to install on each packaging equipment line. These extra steps not only increase packaging equipment costs, but also greatly reduce packaging speeds, increase packaging material waste, and therefore, increase total packaging costs.
An alternative to microporous patches for MAP/CAP of fresh fruits and vegetables is to microperforate polymeric packaging materials. Various methods can be used to microperforate packaging materials: cold or hot needle mechanical punches, electric spark and lasers. Mechanical punches are slow and often produce numerous large perforations (1 mm or larger) throughout the surface area of the packaging material, making it unlikely that the atmosphere inside the package will be modified below ambient air conditions (20.9% O2, 0.03% CO2). Equipment for spark perforation of packaging materials is not practical for most plastic converting operations, because the packaging material must be submerged in either an oil or a water bath while the electrical pulses are generated to microperforate the material. The most efficient and practical method for making microperforated packaging materials is using lasers.
UK Patent Application No. 2 200 618 A and European Patent Application No. 88301303.9 describe the use of a mechanical perforating method to make perforations with diameters of 0.25 mm to 60 mm in PVC films for produce packaging. Rods with pins embedded into the surface of the cylinder are used to punch holes in the film. For each produce item to be packaged, the rod/pin configuration is manually changed so that the number of perforation rows in the film, the distance apart of the rows, the pitch of the pins used to make the holes, and the size of the holes are adjusted to meet the specific requirements of the produce. The produce requirements are determined by laboratory testing produce packed in a variety of perforated films. The invention does not disclose any mathematical method to determine the appropriate size or number of perforations to use with different produce items. In addition, the hole sizes, 20 mm to 60 mm, which are claimed, would be too large to effectively control the atmosphere inside packages containing less than several kilograms of produce. Furthermore, the complicated perforation method would cause lost package production time due to equipment (perforation cylinder) change-overs for different perforation patterns. In addition, the invention cautions that the produce should be placed in the package so that the perforations are not occluded and care should be taken to prevent taping over the perforations in the film. Since the perforations are not registered in a small area on the package, but are placed throughout the main body of the plastic film, the likelihood is high that perforations will be occluded by the produce inside the package or by pressure sensitive adhesive labels applied on packages for marketing purposes. When holes are blocked, the principal route for gas transmission through the film is blocked which leads to anaerobic conditions and fermentative reactions. The result is poor sensory properties, reduced shelf life and possible microbiological safety concerns. Therefore, it is important that perforations be registered in a well-defined area of the package where the likelihood of their occlusion during pack-out, storage, transportation, and retail display is minimized.
U.S. Pat. No. 5,832,699, UK Patent Application 2 221 692 A, and European Patent Application 0 351 116 describe a method of packaging plant material using perforated polymer films having 10 to 1000 perforations per m2 (1550 in2) with mean diameters of 40 to 60 microns but not greater than 100 microns. The patents recommend the use of lasers for creating the perforations, but do not describe the equipment or processes necessary to accomplish this task. The patents describe the limits of the gas transmission rates of the perforated film: OTR no greater than 200,000 cc/m2-day-atm (12,903 cc O2/100 in2-day-atm), and MVTR no greater than 800 g/m2-day-atm (51.6 g/100 in2-day-atm). However, the OTR of a film does not define the total O2 Flux (cc O2/day-atm) needed by a fresh produce package to maintain a desired O2 and CO2 internal atmosphere based on the respiration rate of the specific produce item, the weight of the produce enclosed in the package, the surface area of the package, and the storage temperature. A 50-micron perforation has a very small surface area (1.96xc3x9710xe2x88x929 m2) and a low O2 Flux (about 80 cc/day-atm) compared to its very high OTR ( greater than 200,000 cc O2/m2-day-atm). Therefore, one 50-micron perforation would exceed the OTR limit of this invention. Furthermore, fresh produce items such as fresh spinach are very susceptible to moisture that accumulates inside packages so produce weights greater than 0.5 kg requires 2-3 times more moisture vapor transmission than the upper limit described in this patent.
The above inventions do not address the issue of microperforation occlusion by produce inside the package when microperforations are placed throughout the length and width of the film. Since 20 to 100 micron holes cannot be readily seen with the naked eye, it is impossible to prevent occlusion of the microperforations either by the produce or by adhesive labels applied to the packages when microperforations are placed across and along the entire film. Finally, the size and location of the microperforations in the film also makes it impossible for the packaging user to quickly inspect the films for consistency of perforation size and number. These deficiencies have been roadblocks in the wide spread commercialization of films made according to this invention.
As indicated, the current practices of producing microperforated materials for modifying or controlling the atmosphere inside fresh produce packages are not satisfactory. There is a need for packaging in which the microperforations are registered in a small identifiable area that will not be blocked by adhesive labels or adjacent packages during package stacking or handling. The fresh produce should be placed in a product-specific package where the microperforation size, location, and number of microperforations are optimally selected to obtain the desired film gas transmission rates and gas flux for maintaining the quality of that specific produce item. In addition, a method is needed for accurately predicting the size and number of microperforations required by a particular weight of respiring produce at a specified temperature to maintain a pre-selected atmosphere inside the package during storage. And, there needs to be a cost-effective method of manufacturing microperforated packaging materials according to the requirements of the present invention.
Accordingly, an object of the present invention is to provide a registered microperforated polymeric packaging material with the microperforations situated in well-defined target areas of the packaging material.
Another object of the invention is to provide a means of calculating gas transmission requirements of respiring foods contained in registered microperforated polymeric packaging materials with microperforations having specific size, shape, location, and number in order to optimize the shelf life and quality of respiring foods.
A further object is to provide a packaging system, wherein registered microperforated polymeric packaging materials wherein specific size, type and location of the microperforations is matched to specific characteristics of respiring fresh produce to optimize storage life.
Another object of the invention is the method of manufacturing registered microperforated polymeric packaging materials, using a laser mounted above a stationary or moving polymer film web. The web-handling equipment can be a bagmaking machine, a slitter/rewinder, a printing press, a stand-alone web stopper, or a thermoforming unit. The system of the present invention employs a photoelectric sensor or other electrical means to signal the laser to ensure the microperforations are placed in a small identifiable area on the polymer web. There is a system controller, such as a PLC (programmable logic controller), a PC (personal computer) or a combination of both, that takes the input from the sensor or other electrical signal and commands the laser to fire. The controller may also control the moving web.
This invention is directed to the specification, production, and use of product-specific, registered microperforated polymeric packaging materials selected from the group consisting of polyethylene, polypropylene, polyester, nylon, polystyrene, styrene butadiene copolymers, cellophane, and polyvinyl chloride, in monolayers, coextrusions, or laminates, for extending the quality and shelf life of respiring foods, particularly fresh fruits, fresh vegetables, fresh herbs, and fresh flowers, contained within the packaging.
Another object of the invention is a means of calculating the number of microperforations of a preferred size, for example, 120 to 160 microns, specified for the polymer packaging material to maintain pre-selected levels of O2, CO2, and H2O inside packages containing respiring fresh produce. The calculations can establish the optimal number of microperforations required in the packaging material for each microperforation size and shape.
And yet a further object of the invention is to provide a packaging system for the industry, wherein there is a matching of the packaging material gas transmission rates and the respiration rates of the fresh produce to maintain pre-selected atmospheres inside the packages during storage. The packaging is optimized for a particular item, extending the freshness and quality of the produce.
The present invention is an improved packaging for establishing optimal atmospheric conditions for respiring fresh fruits, vegetables, herbs and flowers, comprising a polymeric material with a set of microperforations in the polymeric material to control the atmosphere within specified O2 and CO2 concentrations in the presence of the respiring fresh produce, wherein the set of microperforations are placed in a registered target area on the polymeric material. The improved packaging material can be used to form a bag or a lidding film or a semi-rigid container.
The present invention is susceptible to many variations, including where the polymeric material is a heat-sealable film. Or where the polymeric material is formed into a semi-rigid container with a thickness in the range of 0.025 cm to 0.076 cm. And, where the polymeric material is selected from the group consisting of polyethylene, polypropylene, polyester, nylon, polystyrene, styrene butadiene, cellophane, and polyvinyl chloride, their blends, coextrusions, and laminates.
The present invention also includes a means of calculating the total O2 Flux (cc O2/day-atm) required by a particular product based on produce weight, respiration rate, storage temperature, and desired gas composition inside the package. The total O2 Flux of the package is satisfied by calculating the O2 Flux provided by the breathable, non-perforated surface area of the packaging material and determining the size, shape, and number of microperforations required to meet the total O2 Flux requirements of the package. In the preferred embodiment, the optimal size, shape and number of the set of microperforations for the particular product is used for the registered target area. In most cases, the target area is a small identifiable area in an upper third or quarter of the package. More preferably, the registered microperforations are placed in any area that will not be occluded by produce or other packages during shipping and storage.
Each of the microperforations has a preferred average diameter between 110 and 400 microns, and more preferably 120-160 microns. It is further desired that the polymeric material that is microperforated have a CO2 transmission rate that is 2.4 to 5.0 times greater than the film OTR, preferably 3.4 to 4 times greater than the film OTR.
The aspects of the present invention include a system of packaging fresh produce comprising the steps of calculating the total O2 Flux required for a given weight of respiring produce item, package surface area, storage temperature, and a pre-selected O2 and CO2 atmosphere. Next, determining an optimal packaging material with a desired CO2/O2 transmission rates wherein the packaging material contains registered microperforations designed for said O2 Flux, placing the produce in the container derived from the packaging material, and hermetically sealing said container.
A further object of the invention is a microperforated packaging for a given quantity of respiring food produced by the process of calculating the number of microperforations for the given quantity of said respiring food, locating a target area for the microperforations, positioning a laser over said target area, and drilling the microperforations in the target area.
Still another object is a microperforation system for making microperforations in a target area of packaging material, comprising a polymeric web, having a laser mounted over the web, a sensor means to identify the target area on the packaging material, and a means to control the laser to drill the microperforations in the target area. Laser drilling software is used to increase efficiency.
The microperforation system can be used on a stationary (stopped) web where the laser beam moves over the packaging material to drill the holes. The laser system is interconnected to a two-axis beam scanner, which directs the laser beam to drill holes in the desired location. Alternatively, the microperforation system can consist of a stationary laser beam and a moving polymer web. The laser is a CO2 laser in the preferred embodiment. In order to provide registration of perforations, a photoelectric sensor is used to find the eye mark on the polymeric film or an electrical signal from the web-handling equipment is used to signal the laser to fire at a preselected location on the film.
A basic intent of the present invention is to make a system for computing an optimal number and size of microperforations to control a package atmosphere within specified O2 and CO2 concentrations. This system also has a means of computing an optimal number of microperforations to control package moisture vapor transmission rates while maintaining pre-selected O2 and CO2 concentrations.
An object of the invention is an improved packaging for establishing optimum atmospheric conditions for respiring fresh fruits, vegetables, herbs and flowers, comprising a polymeric material, a set of microperforations on the polymeric material, wherein the set of microperforations are calculated to control the optimum atmospheric conditions within specified O2 and CO2 concentrations for the respiring fresh fruits, vegetables, herbs and flowers, and wherein the set of microperforations are placed in a registered target area on the polymeric material.
A further object is an improved packaging for establishing optimum atmospheric conditions for respiring fresh fruits, vegetables, herbs and flowers wherein the polymeric material is selected from the group consisting of polyethylene, polypropylene, polyester, nylon, polystyrene, styrene butadiene, cellophane, and polyvinyl chloride, in monolayers, coextrusions, and laminates. Furthermore, an improved packaging material wherein the polymeric material is heat-sealable.
Other objects include an improved packaging material wherein the polymeric material has a thickness in the range of 0.4 to 8 mil. An improved packaging material wherein the polymeric material provides a total O2 Flux ranging from 150 cc/day-atm to 5,000,000 cc/day-atm. An improved packaging material wherein the preferred polymeric material provides a total O2 Flux ranging from 200 cc/day-atm to 1,500,000 cc/day-atm.
And yet another object of the invention is an improved packaging material wherein the polymeric material forms a bag. Also, an improved packaging material wherein the polymeric material is a heat sealable lidding film. An improved packaging material wherein the polymeric material is formed into a semi-rigid container with a thickness greater than 8 mil.
An object of the invention is an improved packaging material further comprising a means of calculating an optimal number of the set of microperforations in the registered target area. An improved packaging material further comprising a means of calculating an optimal size of the set of registered microperforations. Also including an improved packaging material wherein the registered target area is a small identifiable area in an upper quarter of the package. Further objects include an improved packaging material wherein the registered target area is a small identifiable area in an upper third of the package. An improved packaging material wherein the registered target area is located in an area that prevents occlusion of the microperforations by product or other packages. Additionally, an improved packaging material wherein each of the microperforations has an average diameter between 110 and 400 microns, preferably 120-160 microns. Finally, an improved packaging material wherein the polymeric base material has a CO2 transmission rate that is 2.5 to 5.0 times greater than the O2 transmission rate, most preferably 3.4 to 4.0 times greater.
Yet a further object is a system of packaging fresh produce comprising the steps of calculating the total oxygen flux of the polymeric material required for a given weight of respiring produce item, package surface area, storage temperature, and a pre-selected O2 and CO2 atmosphere, determining an optimal packaging material, wherein the packaging material contains registered microperforations designed for the O2 and CO2 transmission, placing the produce in the container derived from the packaging material and closing the container.
An object of the invention is a process of producing a microperforated packaging system for a given quantity of respiring food comprising the steps of selecting a polymeric packaging material for optimal O2 and CO2 transmission rates, calculating a number of microperforations required in the packaging material for the given quantity of the respiring food, locating a target area for the microperforations, positioning a laser over the target area, and drilling the microperforations in the target area.
An object includes a microperforation system for making microperforations in a registered target area of packaging material, comprising, a polymeric web, a laser mounted over the web, a sensor means to identify the target area on the packaging material, a means to control the laser to drill the microperforations in the target area. Additionally, a microperforation system wherein the laser is a CO2 laser. Also, a microperforation system wherein the sensor is selected from the group comprising a through-beam photoelectric sensor and a photoelectric proximity sensor.
And yet another object is a microperforation system wherein a controller directs the laser to drill holes in the target area with the target area identified using an electrical signal from the web-handling equipment. And, a microperforation system wherein the web is moving and the laser is stationary. It being understood that the term laser refers to the laser beams emanating from the laser delivery head or similar delivery device, and the laser optical system provides a focused laser beam.
And another object of the invention is a microperforation system further comprising a means of computing an optimal number and size of microperforations to control a package atmosphere within specified O2 and CO2 concentrations. Also, a microperforation system further comprising a means of computing an optimal number of microperforations to control package moisture vapor transmission rates while maintaining pre-selected O2 and CO2 concentrations. A microperforation system wherein the web is stationary and the laser is moving. And also, a microperforation system wherein the laser comprises a two-axis beam scanner mounted over the web.
A final object is a produce packaging material produced by the process comprising the steps of selecting an appropriate polymeric base material for specified CO2/O2 transmission rates and the quantity of the produce, calculating an optimal number/size of microperforations, locating a target area, positioning a laser over the target area, and drilling the microperforations in the target area with the laser.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only a preferred embodiment of the invention is described, simply by way of illustration of the best mode contemplated for carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention.